Rotary pump with a thermally conductive housing

ABSTRACT

A rotary pump which is suitable for use as the pump for a vehicle power steering system has an integral motor. The pump includes a housing 16 through which a rotatable shaft 4 extends having at one end a pump rotor assembly 5. The pump rotor assembly 5 is in fluid communication with an oil cavity 15 which is in good thermal contact with the housing 16. The housing 16 functions as a heat sink. Mounted on the radially outer wall of the housing 16 is the stator 20 of the motor with the stator 20 also in good thermal contact with the housing 16. The rotor 26 of the motor is located radially outside of the stator 20 and has axially arranged magnets 27. The rotor 26 is connected to the rotatable shaft 4 by means of a radially extending wall 26b. The integral rotary pump and motor is very compact and straightforward to construct and is also capable of withstanding the heat generated by the motor components during the high demands of a vehicle steering system.

This application is a division of U.S. application Ser. No. 08/669,366,filed Sep. 19, 1996, now U.S. Pat. No. 5,810,568, which is a 371PCT/GB95/02621, filed Nov. 6, 1995.

The present invention relates to a rotary pump and particularly to anelectrically driven rotary pump. The present invention is suitable as apump for vehicle power steering but not exclusively so.

Pumps used in power assisted steering of vehicles are usually drivenmechanically directly from the engine. More recently though electricmotor driven pumps have started to be used on vehicles, since they saveengine power and fuel and are easier to package in the engine bay.Conventionally these motors are of the brushed d.c. type, and need to bepowerful enough to satisfy demands for high power at low vehicle speedsand parking. These high power demands, e.g. up to 1 kilowatt account foronly approximately 5% of the operational time of the motor and are shortlived, that is the demand is not expected to last more than ten seconds,for example. Significantly lower power, e.g. 30 to 100 watts, isrequired for approximately 95% of its operational time. Brushless d.c.motors provide better control and can automatically limit in-rushcurrent, unlike conventional motors with brushes. In addition, brusheshave poor performance at very high power and will eventually wear out.Therefore, unlike brushed motors, it is possible to over power abrushless motor for brief periods for a given motor size. Conventionalbrushed and brushless motors consist of a rotating inner wound statorand stationary outer magnets.

The electrical motors used to drive power assisted steering pumps arecommonly mounted adjacent to the pump and require separate assembly andtesting. Moreover, difficulties have been experienced as a result of thevery high temperatures which are generated by the motor especially whenthe higher power demands of low speed steering occur. One solution tothis has been to completely surround the stator of the motor in oil inorder to reduce the temperature of the exterior casing of the motorthereby enabling it to be used safely under the bonnet of the vehicleand preventing failure of its components due to the very hightemperatures generated. This has the disadvantage though ofsignificantly reducing the efficiency of the motor.

It is also the case not only for the above reason but also because ofthe physical limitation on the size of the motor to enable it to bemounted under the vehicle bonnet, that the rotor magnet conventionallyconsists of a rare earth to meet the power demands of the system whichsignificantly increases the cost of the component.

The present invention seeks to overcome at least partly the difficultiesidentified above with respect to conventional motors for power steeringpumps. In this respect the present invention seeks to provide anintegral pump and motor which is compact and yet capable of meeting thepower demands of a vehicle steering system and which reduces theproblems associated with the high temperatures involved in a simple yetcost effective manner.

The present invention provides in a first aspect a rotary pump assemblyhaving at least one inlet port, at least one outlet port, a housing anda pumping device in fluid communication with the inlet and outlet ports,the pumping device including a pump driver member mounted on a rotatableshaft which is connected to the rotor of an electric motor, a portion ofthe housing being located radially between the shaft and the rotor ofthe motor and having the stator of the motor mounted thereon.

The fluid pump includes a cavity in communication with the inlet portwhich may be located about the rotatable shaft.

With the "inside-out" construction described above, that is a stationaryinner wound stator and rotating magnets, more power can be gained for agiven physical size of motor. For reasons of cost and size it ispreferred that a lower rated motor is employed which is capable ofaccommodating the brief demands for high power. With the presentinvention which utilises the "inside-out" construction of a brushlessd.c. motor as described, it is possible to employ a lower rated motorthan has formerly been the case. Ideally means of conducting away fromsensitive components the heat which is generated by such a motor at highpower levels is also provided.

In a preferred embodiment the housing is a heat sink and is in thermalcontact with the copper wound stator of the electric motor. Also thehousing in the form of the heat sink may define at least partially theboundary of the cavity connecting a fluid reservoir to the at least onepump inlet.

In an additional preferred embodiment the circuitry for controlling theelectric motor may be mounted on the pump housing radially between theshaft and the rotor. Ideally the housing is a heat sink and at leastsome of the circuitry may be in thermal contact with the heat sink.

Preferably the rotary pump is integral with the electric motor.

The present invention will now be described by way of example only withreference to the accompanying drawings, in which:

FIG. 1 is a first axial sectional view through an integral rotary pumpand motor in accordance with a first embodiment of the presentinvention;

FIG. 2 is a second axial section view through the integral rotary pumpand motor of FIG. 1;

FIG. 3 is a radial sectional view along the line A--A in FIG. 1;

FIG. 4 is a plan view from above cut-away along the line B- in FIG. 2;

FIG. 5 is a first axial sectional view through an integral rotary pumpand motor in accordance with a second embodiment of the presentinvention; and

FIG. 6 is an axial sectional view through an integral rotary pump andmotor in accordance with a third embodiment of the present invention.

A rotary pump and its associated motor is shown in FIG. 1 and issuitable for use as the pump for a power steering system in a vehicle.The rotary pump and integral motor may be mounted either directly on thesteering rack or gear box of a vehicle or on the chassis near to thesteering rack or on the engine. Indeed, the rotary pump and motor may bemounted anywhere on the vehicle but preferably in the engine bay near tothe steering rack. It is preferred that the rotary pump/motor is near tothe steering system so as to minimise any delay in response to a demandfor power from the steering system and near to the battery to minimiseelectrical losses. The rotary pump is secured by its casing 1 to itsmounting point on the vehicle by means of a locating point at its base1a and two further locating points 2a on a cover member 2. Each of thelocating points may include rubber bushings to limit vibration and noisetransmission.

The rotary pump and motor includes a casing 1 within which is located apump housing 16. A cover member 2 and an oil reservoir 3 are secured tothe pump housing 16. A rotatable shaft 4 is located axially within thecasing 1 and the pump housing 16 and has at one end a pump rotorassembly 5 connected to it. The elements of the pump may correspond tothose of the rotary pump described in U.S. Pat. No. 4,659,296, thecontents of which are incorporated herein by reference although withthis embodiment two inlet ports are provided. The pump rotor 5 isconnected to the shaft 4 by means of spline elements 6 which may beflats, hexagon, key or any other conventional arrangement. To one sideof the pump rotor 5 a port plate 7 is provided which defines the low andhigh pressure ports into and out of the pump rotor. There are two lowpressure ports 8 and two high pressure ports 9 which are shown moreclearly in FIG. 3. The high pressure ports 9 are in communication with adischarge conduit 10 which is provided in the cover member 2 and whichleads to a discharge port 11. The discharge port 11 may be threaded toenable connection to the steering system (not shown). A seal 12 is alsoprovided around each of the high pressure ports 9. To ensure accuratepositioning of the seals 12, the seals 12 may be formed in a single unitand angularly located to the face of the port plate 7 by means of a pin(not shown).

On the opposing side of the pump rotor 5 an end plate 13 is providedwhich locates in a machine recess in the pump housing 16. Fins 14 definethe boundary wall of an oil cavity 15 located about the shaft 4 with theend plate 13 providing inlet ports to the pump rotor from the cavity 15.The fins 14 ensure heat transfer to the oil within the cavity 15 fromthe pump housing 16 which also functions as a heat sink. The end plate13 therefore defines one end of the oil cavity 15, the other end of thecavity 15, distant from the end plate 13, being closed by an oil sealmember 17. Oil is supplied to the cavity 15 by means of an inlet gallery16a, more clearly seen in FIG. 2. Adjacent the oil seal member 17 abearing 18 is provided which may be conventional in design and whichsupports the shaft 4 in position with respect to the heat sink 16 andenables relative rotation of the shaft 4. The shaft 4 rotateshydrodynamically in the bore of the end plate 13.

The pump housing 16 encircles the pump rotor 5, end plate 13, and oilcavity 15 and, as mentioned above, functions as a heat sink. The heatsink 16 may be made of any suitable thermally massive material, forexample aluminium. The heat sink 16 is secured to the cover member 2 bymeans of one or more bolts 19, for example four, or other suitablesecuring devices. The pin (not shown) referred to earlier for locatingthe oil seals 12 to the port plate 7 may be extended to also angularlylocate the cam of the pump and the end plate 13 to one of the fins 14 orto the body of the heat sink 16.

Radially outside of the heat sink 16 is the stator 20 of the electricmotor. The stator 20 is mounted on an outer wall of a first part of theheat sink 16. The windings 21 of the motor, which are usually of copper,are wound onto the stator 20. The stator 20 forms a tight interferencefit to the outer wall of the first part of the heat sink 16. Thus, goodthermal contact is established between the copper wound stator and theheat sink 16. The thermal connection between the stator 20 and the heatsink 16 may also be provided by a thermally conductive material betweenthe stator 20 and the heat sink 16. The windings 21 are connected to acontrol circuit device 22 which is mounted on the end of the heat sink16 distant from the cover member 2. The windings 21 are protected fromthe pump housing or heat sink 16 by means of an electrically insulatingring member 21a.

The control circuitry 22 is provided on a printed circuit board (pcb)which is secured to the heat sink or pump housing 16 by means of one ormore screws 23 or other conventional securing devices. One or more FETs24 form part of the control circuitry 22. In FIG. 1 the FETs 24 aremounted on the lower side of the pcb and are arranged to be in thermalcontact with the heat sink 16 by means of a thermal bridge member 22awhich may consist of anodised-aluminium so that it also functions as anelectrical insulator. Alternatively, as shown in FIG. 5, the FETS may belocated in grooves or channels 25 in the heat sink 16. Either eight orfour FETs 24 are provided with the rotary pump and motor shown in theaccompanying figures, although only two are shown. The FETs 24 arepositioned circumferentially about the heat sink 16.

In the case of FIG. 6 the control circuitry on the pcb 22 is located ina slot in the wall of the casing 1. The FETs 24 in this embodiment aresecured to a thermal bridge 22a which is in contact with the pumphousing 16. Thus, as may be seen in FIG. 6, the control circuitryincluding the FETs is positioned radially outside of the motor and soavoids the overall axial length of the integral pump and motor beingincreased.

Radially outside of the stator 20 is provided the rotor 26 therebyforming a brushless motor. The rotor 26 has an axially extending wall26a to which the magnets 27 are secured by any suitable adhesivematerial such as a cement mixture. The arrangement of the magnets 27 isconventional in the form of alternate segments of magnets havingdifferent poles. Conventionally 14 segments are employed. At one end ofthe axially extending wall 26a of the rotor 26 there is provided aradially extending member 26b which connects the axially extending wall26a to the shaft 4. At the end of the radially extending member 26badjacent the shaft 4 an aperture through which the shaft 4 passes isdefined by a shaft engaging wall 26c. The shaft 4 is held by the shaftengaging wall 26c in a press fit. A bearing retainer or collar 40 mayalso be provided.

As shown in FIGS. 1 and 2, the space axially outside of the rotor 26 butwithin the casing 1 can be used to hold additional control componentsfor example filter capacitors 42 for use in the suppression of powerspikes. The power leads 41 are shown extending from the stator 20 aroundthe outside of the rotor 26 to the filter capacitors 42. An internalcable shield 44 prevents contact of the leads 41 with the rotor 26. Thecapacitors 42 are connected in parallel between the positive andnegative power connections 43 which also provides the control input.

In FIG. 6, it will be seen that the filter capacitors 42 and additionalcontrol components are positioned with the pcb 22 radially outside ofthe motor. The electrical connections 43 are similarly provided on thecasing distant from the rotor 26.

With reference to the upper portion of FIGS. 1, 2, 5 and 6, the covermember 2 and oil reservoir 3 is generally conventional in design. Thereservoir 3 is arranged to hold 1/2 liter of oil. A closable aperture 28is provided at one end of the reservoir 3 to enable oil to be removedand added. A screw threaded lid member 29 is shown in FIG. 1. Thereservoir 3 also includes a vent 29a to accommodate oil volume or fluidlevel variations. An oil return port 30, marked in FIG. 1 in dottedlines, provides the inlet port for oil returning from the steeringsystem. The returning oil then passes through a ring filter 31 which issecured at one end to a sprung plate 32 which acts as a pressurelimiter. The sprung plate 32, which is in the form of fingers to permitoil from the main body of the reservoir 3 to feed to the pump, isarranged to raise the filter 31 from its position against a projectingwall 33 of the cover member 2 in the event the filter 31 becomesblocked. In this way oil entering the return port 30 may pass downstreamof the filter 31 in the event, for example, a pressure in excess of 1/2bar develops upstream of the filter 31. The filter 31 may beconventional in design consisting of a paper element secured at each endto steel or rubber end caps 34. Alternatively, the filter 31 may beconstructed from nylon mesh.

The oil reservoir 3 is connected to the cover member 2 through at leastone O-ring 35. The reservoir 3 is secured to the cover member 2 by meansof a snap fit over lugs 2b formed on the periphery of the outer wall ofthe cover member 2. A similar O-ring 36 is located in a groove in theface of the heat sink 16 which abuts against the cover member 2.

Pressure relief valve means 37 is provided to bring the high pressuredischarge conduit 10 in communication with the low pressure inletgallery 16a, when the pressure of the oil emerging from the highpressure ports 9 exceeds a predetermined value. The inlet 38 to thepressure relief valve 37 therefore communicates with the high pressureconduit 10 and the pressure relief outlets 39 communicate with the oilreservoir 3.

In FIG. 1 the high pressure ports 9 and the high pressure dischargeoutlet 11 is shown. In FIG. 2, on the other hand, the communication ofthe oil cavity 15 with the low pressure ports 8 is shown. The lowpressure galleries 16a are shown and, as may be clearly seen, thegalleries 16a are defined by the wall of the heat sink or pump housing16 and the rotary pump assembly. The inlet galleries 16a provide thefluid connection between the reservoir 3 and the cavity 15.

It will be appreciated that unlike conventional motors used with rotarypumps, the rotor 26 is positioned and rotates on the outside of thestator 20. Moreover, at least part of the pump housing is locatedbetween the shaft and the rotor 26. This arrangement provides a numberof significant advantages over conventional arrangements of rotary pumpsand motors. Firstly, the stator 20 of the motor is in thermal contactwith the heat sink 16 which is, in turn, in thermal contact with oil inthe cavity 15. Heat generated from the stator 20 is thereforetransferred to the oil which is then pumped around the steering systemwhere it is cooled. Similarly the FETs 24 are also in thermal contactwith the heat sink so that the heat generated may be transferred to theoil. This significantly reduces the temperature of the casing 1 therebyenabling the rotary pump and motor to be used under the bonnet of avehicle safely and more significantly maintains the internal componentsbelow a temperature which could cause failure.

Also, because the rotor 26 is on the outside of the motor it is largerthan conventional rotors and enables the rotor magnets to be made of aferrite material rather than a rare earth for a given power.

In the case of FIGS. 1 to 5, the fact that the control circuitry 22 iswithin the enclosed space of the rotor 26 protects the control circuitry22 from damage and also provides electrical and magnetic shielding ofthe control circuitry. The casing 1 provides additional shielding. Italso allows for a single control/power connection to the outside of thecasing 1, as desired. In the embodiment of FIG. 6, the control pcb 22 ismounted externally of the rotor 26 but still within the motor casing 1.This too enables the pump and motor to be built and tested as a discretepower unit.

As may be seen clearly in the Figures, the arrangement described alsoenables the rotary pump to be positioned at least partially and ideallywholly within the axial and radial dimensions of the motor. This resultsin a significantly smaller pump and motor unit in which the pump isintegral with the motor by means of the heat sink 16. This also enablesthe pump and motor to be manufactured as an integral unit requiring oneset of tests rather than individually testing the pump and motorseparately.

It will be appreciated that the pump assembly need not consist of apumping device in the form of vanes with a rotating carrier andassociated cam member. Alternatively, the pumping device could consistof two or more gears or a piston with a swash plate or cam mounted onthe rotatable shaft.

Alternative arrangements and functionally equivalent components areenvisaged whilst remaining within the spirit and scope of the presentinvention claimed in the accompanying claims.

We claim:
 1. A rotary pump assembly for automotive vehicles having atleast one inlet port; at least one outlet port; a pumping device influid communication with and for circulating a fluid between the atleast one inlet port and the at least one outlet port, the pumpingdevice including a pump driver member mounted on a rotatable shaft; anelectric motor having a rotor and a stator, the rotor being connected tothe rotatable shaft with the stator positioned between the rotor and therotatable shaft; and a heat sink on which the stator is mounted, theheat sink being in thermal contact with the circulating fluid wherebyheat from the stator is transferred by the heat sink to the circulatingfluid and wherein the heat sink forms part of a housing of the pumpingdevice and isolates the circulating fluid from the region between thestator and the rotor.
 2. A rotary pump as claimed in claim 1, wherein atleast one electrical component for controlling operation of the electricmotor is in thermal contact with the heat sink.
 3. A rotary pump asclaimed in claim 2, wherein the at least one electrical component ispositioned radially outside of the rotor.
 4. A rotary pump as claimed inany of the claim 1, wherein the heat sink consists of a plurality ofmembers in thermal contact with one another which provide a thermalbridge from the stator to the circulating fluid.
 5. A rotary pump asclaimed in claim 1, wherein the heat sink includes a plurality of finson a surface in contact with the circulating fluid.
 6. A rotary pump asclaimed in claim 1, wherein the heat sink is in thermal contact with thecirculating fluid between a fluid supply and a pump outlet.
 7. A rotarypump as claimed in claim 1, wherein the rotor is connected to therotatable shaft by means of a radially extending member and wherein theradially extending member is connected to an end of the rotatable shaftdistant from the connection of the rotatable shaft to the pump drivermember.
 8. A rotary pump as claimed in claim 1, wherein the pump drivermember is a positive displacement pump.
 9. A rotary pump as claimed inclaim 1, further including a fluid cavity located between the rotatableshaft and the stator for connecting the fluid supply to the pump drivermember.
 10. A rotary pump as claimed in claim 9, wherein the fluidcavity is partly defined by a portion of the heat sink.
 11. A rotarypump as claimed in claim 1, wherein the heat sink is common to both thepumping device and the electric motor.
 12. A rotary pump as claimed inclaim 1, arranged for use in a vehicle powered steering system.